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Sprinter RV's & Conversions Talk Common features found in Sprinter RV's and Conversions.


 
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Old 01-13-2019, 10:44 PM   #1
NobleOne
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Default Can a lithium pack be charged by alternator alone?

I have a T1N with a 150 amp alternator, which I understand to be more forgiving as far as using the alternator to charge the house batteries than the later Sprinter models. I know lead acid batteries must be full recharged, and that lithium batteries donít require such (some reading indicates that they might actually live longer). This seems to lend itself to the possibility of recharging such a pack via alternator alone...no solar involved. Is that reasonable and feasible using these?
http://www.lithiumrvbattery.com/Lith...0AH_Cells.html
Or am I missing some key bit of information?
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Old 01-14-2019, 01:59 AM   #2
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Default Re: Can a lithium pack be charged by alternator alone?

Yes, LFP is very fast, no need to get to Full.

But put a Sterling BB series DCDC charger in between to protect your alt setup and give the LFP its custom setpoints.
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Old 01-14-2019, 04:43 AM   #3
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Default Re: Can a lithium pack be charged by alternator alone?

If your LFP is bigger than around 50Ah it will suck very hard on your alternator.

I started off with a 50Ah LFP bank, and if its got mid to low SOC it will easily pull 80A from the alternator. So a 100Ah bank like that would pull double and your car voltage will sag badly.

I now have a 160Ah bank and have put a 30A DCDC charger between it and the alternator, just to stop that from happening.

You also dont want to be holding 14.2V on the bank once it is fully charged, so you need to be able to disconnect it from the alt on long drives. A decent DCDC will effectively do this for you automatically if set up properly.

Last edited by owner; 01-14-2019 at 04:47 AM.
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Old 01-14-2019, 05:31 AM   #4
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Default Re: Can a lithium pack be charged by alternator alone?

Quote:
Originally Posted by owner View Post
If your LFP is bigger than around 50Ah it will suck very hard on your alternator.

I started off with a 50Ah LFP bank, and if its got mid to low SOC it will easily pull 80A from the alternator. So a 100Ah bank like that would pull double and your car voltage will sag badly.

I now have a 160Ah bank and have put a 30A DCDC charger between it and the alternator, just to stop that from happening.

You also dont want to be holding 14.2V on the bank once it is fully charged, so you need to be able to disconnect it from the alt on long drives. A decent DCDC will effectively do this for you automatically if set up properly.
Did you try to charge your 160aH bank without the B2B charger in place?
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Old 01-14-2019, 06:27 AM   #5
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Default Re: Can a lithium pack be charged by alternator alone?

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Did you try to charge your 160aH bank without the B2B charger in place?
I have a 4 way switch that does allow direct alternator charging if I need it but I havent been game to switch it to that position with low soc on this big bank. I imagine it would pull everything it could from alt until the 100A thermal breaker kicks in.
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Old 01-14-2019, 07:00 AM   #6
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Default Re: Can a lithium pack be charged by alternator alone?

I had the optional heavy duty alternator and initially could never get more than about 60A into a 320AH battery. After I upgraded the alternator ground wire, a lot of the factory battery cables and battery grounds I could get 100A.
The limiting factor for very high current charging is the net resistance of all the wires to and from the battery.
With factory wiring I do not think you could get over 80A, which is likely a good thing since it will limit the load on the alternator.
But...
You do need a way to turn it off. Once it is charged at about 14.2 to 14.4V (read your battery spec or watch for the voltage where the current starts to drop quickly). Then you should disconnect the alternator. Lithium does not like to be kept at max voltage and float charged. It won't be destroyed but the lifetime will be decreased.

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Old 01-14-2019, 02:56 PM   #7
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Default Re: Can a lithium pack be charged by alternator alone?

What about the Orton method? Would that overcome those listed concerns/limitations? I would like to use a 300 or 400 ah setup.
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Old 01-14-2019, 07:01 PM   #8
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Default Re: Can a lithium pack be charged by alternator alone?

?? As I recall, Orton used the BtoB method with the controller / converter??

I can't comment other than to say that I think the Sprinter alternator cables and ground are inferior. As I recall they are #2 wire with a fairly long run from the alternator to the battery. In my Sprinter, they also added a 3' piece to connect to the factory battery isolation relay that could be replaced with a 6" piece.

I could never find the "official" answer but I believe that the voltage regulation point is the alternator terminal. So based on air temperature you will have around 14.3V between the alternator case and the alternator output. At 100A you will loose .16V for every 10 foot of #2 wire not counting the voltage drop of each connection. The wiring / location needs to be such that you can sink the current you desire from roughly 14.3 at the alternator.

Any eye opening experiment is to load the alternator as high as you can and then run around and measure voltages to the chassis. This includes the voltage of the alternator case, voltages on each side of a connector and voltages on each side of the isolation relay.

It is hard to get a reliable 100A in a 12v system.

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Old 01-14-2019, 07:10 PM   #9
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Default Re: Can a lithium pack be charged by alternator alone?

I get somewhere around 70-80a from alternator directly to 300ah lithium battery via double 2ga wires (so equivalent to 0ga?) running 12'. Good enough for me and I don't use it much at all since I have solar.
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Old 01-14-2019, 07:33 PM   #10
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Default Re: Can a lithium pack be charged by alternator alone?

Quote:
Originally Posted by RonR View Post
?? As I recall, Orton used the BtoB method with the controller / converter??
http://www.ortontransit.info/electric.php
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